Kim Jong Un escalates nuclear threats as US carrier arrives in South Korea.

North Korea unveiled new, smaller nuclear warheads and vowed to produce more weapons-grade nuclear material to expand the country’s arsenal, as a U.S. aircraft carrier arrived in South Korea for military drills. Experts say the images could indicate progress in miniaturizing warheads that are powerful yet small enough to mount on intercontinental ballistic missiles capable of striking the U.S. Pyongyang has accused the allies of stoking tensions and using exercises to rehearse an invasion.